Bright copper plating



Patented Dec. 18, 1945 PATENT OFFICE amour corrnn rm'rmo John F. Beaver, Jr., Dayton, Ohio No Drawing. Application September 15, 1941,

4 Serial No. 410,853

2 Claims.

This invention relates to bright copper plating, and particularly to ornamental or decorative bright copper plating from an acid bath.

I have discovered that in contradiction of accepted practice, I am able to electrodeposit an ornamental bright copper plate on metal articles in. an acid bath and obtain a plate of high covering or smoothing power and high throwing power with high cathode efllciency using a plating solution characterized by its long life and high tolerance of impurities.

Hitherto acid copper plating baths have been used chiefly in electrotyping, electroforming and for immersion copper coating using current densities of from.15 to 40 amperes per square foot, a voltage of from 0.75 to 2.0, and a temperature of from 75 to 120 F. It is known that more rapid deposition is possible if air agitation is used, and in such cases, the bath concentration is usually increased, the bath is warmed, and current densities of from-75 to 150 amperes per square foot are employed.

Acid copper plating baths, however, have not been considered suitable and have not been used commercially 'for bright copper plating. Cyanide copper solutions have been almost universally used fOr thin deposits for ornamental finishes, flashing of iron or steel prior to heavy copper deposits in the acid copper bath, and for plating an undercoat for other metals. In all these applications the current densities were not over 10 amperes per square foot, usually less, and While a cathode emciency of 60% or better was a possibility, actual plant values were quite variable and astonishingly low.

Recognition of the value of heavy copper deposits under nickel and chromium on zinc base die casting and elsewhere emphasized the limitation of the conventional cyanide bath and stimulatedthe development of the relatively new Rochelle salt type bath. With its development the demand for high speed was satisfied and attention was directed then toward improving the brightness of the deposited copper in order to eliminate bufflng prior to bright nickel and chromium plating. It will be understood that where bufllng is required a greater thickness of copper is necessary in order to avoid the danger of cutting through the plate while bufling.

In spite of the decided advantages of the R0- chelle salt type bath over the conventional copper cyanide bath, the bright copper plating bath and method of my invention offer decided advantages as compared with the hitherto known baths and methods. For instance, proper operation of the conventional copper cyanide bath requires a temperature of 75 to 100 F., a current density of 2.5 to amperes per square foot, and a voltage of from 1.5 to 2 with a maximum cath- 5 ode efilciency of about 60%. Likewise, operating conditions of the Rochelle salt type bath require a temperature of 140 to 160 F., a current density of to 60 amperes pe square foot, and a voltage of from 2 to 3 with a cathode efiiciency of The bright copper bath of my invention operates satisfactorily at' a temperature ranging from below '90 to more than 120 F. The average current density is 100 amperes per square foot with a minimum of from 75 to 80 and a maximum in excess oi. 200 and a voltage of 2 to 3 with a cathode efilciency of 98 to 100%. Of course, the minimum and maximum practical current density will depend on the composition of the bath.

20 Furthermore, the plating bath and method of my invention are characterized by extremely high throwing power and the ability to plate over surface defects whereby a smoothening action is obtained which results in a higher grade of lated article particularly well adapted to receive a secondary coating of some other metal as, for instance, bright nickel or chromium.

By way of example and without thereby limiting my invention to the particular details set forth, I shall now give a typical outline of the method followed and plating bath used in a particularcase for plating a bare steel article.

remove 3 ounces of free sodium cyanide, and 2 to 8 ounces of sodium carbonate.

5. The cyanide plated article is rinsed with water to remove cyanide.

Brzght plating The bright plating solution may-comprise, for example, 26 ounces per gallon of copper sulfate (01180451320) and 6.5 ounces per gallon of sul- 3 to 5 ounces of copper metal per gallon, 1 /2 to phuric acid. Such a solution will have a pH value of approximately 1.

In addition, the solution will contain a brigthener. 'I'hiourea has been used as a brightener in the course of my investigation, but it has the disadvantage of not holding up in the plating bath. Aryl and alkyl substitution products of thiourea such as thiourethane, phenyl thiourea, diphenyl thiourea, benzyl thiourea and hemethiourea have also been used with satisfactory results, although all of them have certain faults. Propyl, acetyl, hydrochloride, nitrate and metal salt derivatives or thiourea have also been used satisfactorily. V v

I prefer to use the acetyl derivative in proportions of from 0.005 to 0.1 ounce per gallon.

Furthermore, a small quantity of wetting agent should be added to the bright plating solution. I

have used a wide variety of commercial wetting agents,

including, for example. Duponol-80, Duponol-WA, Duponol Special-WA paste, Alkanol-SA, Triton and sodium lauryl sulfate in proportions of approximately 0.3 ounces per gallon. It is generally understood in the art Duponol-80 and Duponol-WA are sodium salts of sulfated alcohols, that DuponolSpecial-WA paste is a sodium salt of sulfated alcohols containing oetyl compounds, that Alkanol-SA is isopropyl naphthalene sulfate, and that Triton is a high molecular alcohol.

In addition, the bright copper solution may contain small quantities or agents adapted to permit higher current densities. For instance, dextrin, sugar and sulfonated creosote are typical examples.

"The article to be bright plated after receiving the preliminary treatment above described is immersed in the bright copper solution for the time required for the desired degree of brightness. For instance, two minutes immersion sufiices for a plate of from 1.5 to $5 inch (depending on the current density). In a present practice of my invention, a commercially acceptable bright surface is obtained using a solution including 0.02 ounce of acetyl thiourea, 0.30 ounce Duponol Special-WA paste, and 0.25 ounce of dextrin at a temperature of 110 F. with a plating time of live minutes with cathode agitation. When a new solution is being started, it is advantageous to add to it approximately 0.03 ounce per gallon of 100 volume hydrogen peroxide.

It will be understood that I do not limit mysell to the particular formulation above indicated. The following are further typical examples of formulations I have successfully used in commercial practice according to my invention:

Example I Ounces per allon Copper sulfa 26.00 Sulphuric acid 6.50 Acetyl thiourea 0.02 Duponol Special-WA paste 0.30 Dextrin 0.25 Hydrogen peroxide (100 vol.) 0.03

Example II Ounces per gallon Copper sulfate 26.00 Sulphuric acid 6.50 Acetyl thiourea 0.01 Sodium lauryl sulfate"; 0.30 sulfonated creosote 0.25

Example 111 Ounces Per gallon Copper sulfa 26.00 Sulphuric acid 6.50 Acetyl thiourea 0.02 Duponol-80 0.80

Example IV Ounces per allon Copper sulfa 15.00 Sulphuric acid 4.50 Acetyl thiourea-- 0.01 Sodium lauryl sulfate 0.30 Dextrin 0.25

Example V I Ounces per 7 gallon Copper sulfa 30.00 Sulphuric acid 7.50 Acetyl thiourea 0.02 Duponol-WA 0.30 Dextrin 0.30 Hydrogen peroxide 100 vol.) 0.03

Example VI Ounces per gallon Copper sulfate 26.00 Sulphuric acid 7.00 Acetyl thiourea 0.01 5 Alkanol-SA 0.30 Dextrin 0.30 Hydrogen peroxide (100 vol.) 0.03

Example VII 40 Ouncesper gallon Copper sulfate 80.00 Sulphuric acid 0.00 Acetyl thiourea"-.. 0.02 Triton 0.30 Sodium lauryl sulfate 0.30 Dextrin 0.30

Example VH1 Ounces per gallon Copper s lf 30.00 Sulphuric acid e 6.00 Acetyl thiourea 0.02 Phosphoric a 1.50 Duponol Special-WA paste 0.30 Dextrin 0.30 Hydrogen peroxide (100 vol.) 0.03

Example IX Ounces per gallon Copper sulfate 26.00 Sulphuric a 5.50 Phosphoric acid 1.00 Acetyl thiourea 0.02 5 Duponol-WA 0.30 sulfonated creosote.... 0.25

Example X Ounces per gallon Copper sulfa 30.00 Phosphoric acid 7.50 Acetyl thiourea 0.02 Duponol Special-WA paste 0.30 Dextrin 0.80 Hydrogen peroxide vol.) 0.03

Exampl x1 Ounces per gallon Copper sulfa 80.00 Phosphoric a 8.00 Acetyl thiourea 0.02 Triton 0.30 Sodium'lauryl sulfate.. 0.30 Dextrin 0.30

Example XII Ounces per gallon Copper sulfate 15 Phosphoric acid--- 4.50 Acetyl thiourea 0.01 Sodium lauryl sulfate 0.30 Dextrin 0.25

It is well to point out that as the temperature Furthermore, as the concentration of bright: ener in the bath increases the hardness of the of the bath increases the permissible current plate and its brightness also increase but the throwing power is reduced. As the time of plating increases the thickness.

and smoothness of theplate will increase and as the surface tension of the solution is reduced the throwing power or bright range of the bath is increased.

As will be noted from some of the examples given hereinbefore, phosphoric acid may be substituted to good advantage for a portion of the sulphuric acid in the formula. For example, the amount of sulphuric acid'may be 5.50 ounces per gallon together with phosphoric acid in the amount of 1.00 ounce per gallon. This addition of phosphoric acid or substitution of a portion of the sulphuric acid by phosphoric acid results in increasing the throwing power of the plating bath of my invention, and in the case of some specific articles, this is a very valuable attribute.

As has hereinbefore been mentioned, the plating bath of my invention is characterized by the fact that it permits a cathode efliciency of 98 to 100% together with extremely high current densities. p

In the case of plating brass or copper the cranide copper plating hereinbefore described in the case of a 'bare steel article is omitted.

In the commercial practice of my invention metal articles of various shapes intended for various purposes are handled. It is common practice to subject. such articles to bright copper plating substantially as outlined in the typical procedure hereinbefore first described. An article subjected to such treatment for a period of substantially nve minutes is characterized by a smooth. hard and extremely homogeneous bright surface free plated according to my invention are subjected to bright nickel plating for a period of only one minute and the resulting plate is characterized by a smoothness and brightness of surface far superior to that obtainable by straight bright nickel plating for six minutes under standard conditions. a

Bright copper plated articles commercially plated according toomy invention for a period of substantially five minutes are also regularly subjected .to bright nickel plating for a period of one minute followed by chromium plating for a period of substantially ten to fifteen seconds. The resulting chromium plate is characterized by extreme brightness and homogeneous texture and is far superior in appearance to a chromium plate deposited on a similar article having had a previous plating treatment comprising six minutes of bright nickel plating. v v

- As is well known to those skilled in the art, copper sulfate and sulphuric acid are preferred for use in the plating bath of my invention because of their low cost. However, other copper salts and other inorganic acids may be used in place of copper sulfate and sulphuric acid so far as the operative technique and results are concerned.

It, will be understood that while I have herein my invention, it is not my intent to have my invention limited to or circumscribed by the specific details of proportions and procedure herein set forth, since my invention may be varied widely within the spirit of this disclosure without departing from the scope of the appended claims.

I claim:

1. A bright copper plating bath comprising copper sulfate, sulfuric acid, a brightener in proportion of from 0.005 to 0.1 ounce per gallon, said brightener being selected from the group consisting of aryl and alkyl substitution products of thiourea and acetyl, hydrochloride, nitrate and metal salt derivatives-of thiourea,a wetting agent in proportion of approximately 0.3 ounce per gallon, said wetting agent being selected from the group consisting of sodium salts of sulfated alcohols, sodium salts of sulfated alcohols which contain cetyl compounds, isopropyl naphthalene sulfate, sodium lauryl sulfate and a substance 7 adapted to permit high current densities in progallon of sulfuric acid, substantially 0.01 to 0.02

' ounce per gallon of-acetyl thiourea, substantially from burned edges, and particularly well adapted for receiving a secondary plate of other metal.

For instance, some of thearticles commercially 0.3 ounce per gallon of sodium lauryl sulfate, substantially 0.25 ounce per gallon of dextrin, a maximum of substantially 0.03 ounce per gallon of volume hydrogen peroxide and a maximum of substantially 1.5 ounces per gallon of phosphoric acid.

JOHN F. BEAVER. Js. 

